Protien Turnover And Catabolic Disease Flashcards
Tagging Ubiquitin to a protein substrate
Ubiquitination
E1-> Ubiquitin activating enzyme -> activates Ubiquitin forming a thioester bond between C terminal glycine of Ubiquitin and an internal cystine of E1. >500 types
E2-> Ubiquitin conjugating enzyme -> Ubiquitin is transferred to E2-> facilitates transfer of Ubiquitin to the protein substrate specifically selected. 30 types
E3-> Ubiquitin protein ligase -> specifically selects the protein substrate-> covalent attachment of Ubiquitin to a lysine residue in the protein substrate. 2 of them
Target is often polyubiquitinated
Released after ubiquitination
Specificity due to diversity of E3 and E2/3 interactions -> combination determines which Ubiquitin chain is formed
Ubiquitin proteasome system
Targets intracellular protiens for degradation by covalently binding to the t-amino acid Degradation by 26s proteosome Nucleus and cytoplasm 76 AA protein which is highly conserved ATP dependent Short lived intracellular protien
Degradation of the protein
Degraded by a proteosome -> cylindrical 20s protein with multiple internal proteolytic sites
Protein is unfolded and pushed into the core via ATP hydrolysis
Regulated by cap protein complexes-> bind ubiquinated protiens using ATP and deliver them to the proteosome
Produces digomers which are further degraded to amino acids
Ubiquitin is recycled
Structure of the proteosome
20s-> proteosome-> catalytic activity-> 2a and 2b chains
19s cap protien complex-> lid and base-> specifics, binding and unfolding
-> 6 ATPs in base provide energy
-> Ubiquitin tag removed
Ubiquitin receptors
-> Ubiquitin associated domain-> binds chain
-> Ubiquitin like domain-> binds C95
Autophagy
Cytoplasm Longer lived, bulkier protiens Organelles and protien aggregates broken down Degradation in lysosomes 1) chaperone mediated 2) microautophagy 3) macroautophagy -> autophagy
Induction of autophagy
Internal and external stimuli -> starvation
Inhibited under nutrient rich conditions-> amino acids, glucose
mTOR inactivation by starvation-> downstream dephosphorlyation-> transcriptional activation of autophagy genes
Via ULK1/Atg13
Autophagosome formation
Nucleation and expansion
Double membrane forms, possibly from rough ER with Atg protien participation
Nucleation:
Atg1/unc-51 complex produced by dephosphorlyation
mATG9
Vsp34/class III phosphatdylinostitol-3 kinase complex one-> PI3P
Expansion:
Atg 12 and Atg8/MAP1 light chain 3(LC3II) -> Ubiquitin like proteases
LC3II produced by Atg 3,4,7
-> phagophore
-> fully surrounded by double membrane-> Autophagosome
Autophagosome fusion and breakdown
Autophagosome either developes micro tubules or an endosome (becomes a amphisome)
-> fuse with lysosome-> auto lysosome
Contents of Autophagosome released in to lysosome for degradation
Autophagosome membrane is then also degraded
Selective autophagy
Non selective is starvation induced Selective-> recognition of proteins to be degraded -> aggregphagy-> protein aggregates -> mitophagy-> mitochondria -> xenophagy-> bacteria and macrophages
Ubiquitination in selective autophagy
Control of autophagy or protiens of the Autophagosome machinery
Facilitate recruitment of autophagy adapters or Ubiquitin receptors -> adapters contain a Ubiquitin binding domain and a LC3 interacting region-> can link to autophagic machinery
Ly63 Ubiquitin chains-> for autophagy
p62 and NBR1-> autophagic receptors
Proteinopathies
Cause neurodegeneration
Abnormal aggregation of protein inside and outside surviving neurones
Parkinson’s-> Lewy bodies -> intra neuronal a synuclien
Alzheimer’s-> tangle-> intraneuronal-> MAP tau
-> extra neuronal-> AB
Proteostasis
Controls concentration 3D structure, binding interactions and sub cellular or extra cellular location of proteins
Protienopathies and defective protein turn over
Miss folded proteins first recognised by chaperones-> help the protein fold properly
If the chaperone can’t help-> broken down by proteosomes
If both processes are overwhelmed-> aggregated proteins produced
Aggregated proteins inhibit proteosome activity
Proteosomes and autophagic activity decrease with age
UBB+1 in polyubiquitin inhibits proteosome activity-> increases with age, caused by a mutation in Alzheimer’s
Parkinson’s
Proteasomal and autophagic degradation Parkin E3 Ubiquitin ligase Produces lys48 and lys 63 Ubiquitin chains Aggregphagy and microphagy Familial Parkinson's
UCHL1 debubiquinating enzyme
Abudant in neurones E3 ligase activity when dimerised Oxidised in Parkinson's and Alzheimer's Also P97/valosin in containing protein -> mutation/loss of VCp-> Ubiquitin pathology -> should be p62 which activates UBA/UBL
